why can't I put spaces between my paragraphs?

Hello, I'm trying to put spaces in between my paragraphs and I'm having difficulty. It works while I'm in editing, but when I hit "publish" or "save" or "save and continue editing," and view my blog, the spaces are gone, and my paragraphs are all pushed together. When I return to re-edit the post, there is no evidence of my having made any changes.